In many parts of the United States, wastewater run-off from storm events is allowed to flow into natural waterways. However, particularly in urban areas, this wastewater is likely to entrain relatively innocuous particulate materials, such as sand, gravel and potentially more objectionable particulates such as hypodermic needles and all manner of garbage. This can result in the discharge of highly undesirable debris into natural waterways.
The problem described above is exasperated in those areas having combined wastewater and sewage conveying systems. As used herein “wastewater” shall mean either storm run-off or combined sewage and storm run-off. Combined conveying systems are particularly common in the eastern half of the United States. During times of moderate precipitation, the combined storm wastewater and sewage can be treated at existing sewage treatment plants. However, when exceptional storm events occur, sewage treatment plants can become overwhelmed and it is necessary to release combined and untreated wastewater and sewage to natural waterways.
Many parts of the country have laws requiring removal of particulates greater than a select size from wastewater or combined wastewater/sewage flows before they can be discharged into a natural waterway. For example, New Jersey has mandated removal of particulates greater than 0.5 inch in size.
One known technology for particulate removal is offered by Fresh Creek Technologies. This technology uses a mesh bag that floats at the end of a pipe or in-line with a stream of wastewater. The bag collects solids and floatable materials of a size to great to flow through the mesh. Once the bag is full, a maintenance truck removes the bag to a landfill.
This mesh bag technology has several serious deficiencies. First, debris collected in the bag can create significant headloss by limiting the cross-sectional flow area and creating additional force upon the bag. If sufficient force is developed, this can damage the bag or otherwise result in a release of unacceptable solid and floatable materials to the natural waterway. Second, the nets are also unsightly and can lead to odor problems. Third, rodent activity, prevalent in sewer and conveying systems, can create tears in the bags that would result in a release of unacceptable solid and floatable materials to the natural waterway. The disposable bag also exacerbates waste disposal issues.
It is well known in the art that sieves or screens can be used to remove particulates from a liquid flow. However, known screening systems have a problem with debris buildup that can obstruct the flow of wastewater through the screening system during a storm event. This can lead to serious problems, including sewage backups in the conveying system that can result in the undesired discharge of unscreened wastewater through upstream catch basins and manholes to the natural waterway.
Eimer, U.S. Pat. No. 4,680,113, teaches a sieve arrangement for recovering cleaning particles from a cooling water stream downstream of a heat exchanger. The sieve arrangement taught by Eimer includes a screen or sieve across a flow of discharged water which is inclined relative to the discharged water flow. The screen is sized to collect cleaning particles on a leading surface. Eimer teaches providing a baffle in the water flow which creates a vortex impinging downward in a vertical direction on the cleaning particles to direct the cleaning particles downward into a recovery conduit. While suitable for the removal of these cleaning particles for reuse, such a system is not effective for wastewater solids removal because of the difficulty in continuously extracting solids of non-uniform size and shape likely to be encountered in wastewater runoff.
The present invention is directed toward overcoming one or more of the problems discussed above.